The use of phytoliths as a proxy for distinguishing ecological communities: A preliminary phytolith reference collection for the mountains of Dhufar, Oman

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The Ohio State University

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The Dhufar Mountains region of Oman has high ecological diversity, circumscribed by distinct landscape zones, largely due to the effect of waning summer monsoon cloud precipitation. The Ancient Socio-Ecological Systems in Oman (ASOM) project uses a coupled human and natural systems approach to study the emergence of territoriality in pastoralist systems in Dhufar using a multitude of datasets and proxies. One such proxy are phytoliths, silicon dioxide microfossils formed in the cellular and intercellular spaces of living vascular plants. These sediment components remain in soils following the death and decay of above-ground plant tissue and as a result can be used in the study of past vegetation community dynamics. Due to uneven rates of phytolith formation based on plant family and small potential for post-burial contamination, it is best to document phytoliths at the community-level. My study addressed the differences in phytolith morphotypes and densities of the tallgrass savannah and inner-Nejd plant communities of Dhufar, two communities that reflect variation in vegetation structure and composition. For robust analysis, I created a reference collection of these two communities to detect possible morphotypes indicative of specific taxa and differences in phytolith production. To reduce the total sample set to the most meaningful types, I selected among all plants identified in botanical surveys by two criteria: 1) those most indicative of the circumscribed zones according to multiple classifications, and 2) high phytolith producing potential. Phytoliths were extracted from the leaves of each specimen via dry-ashing and phytolith densities and morphotypes were then assessed by counting under a microscope. The results indicated that phytolith density was not a distinguishing characteristic between the tallgrass savannah and the inner-Nejd zone, but that the number of phytolith types produced by each community was significantly different. Many trends in lobate abundance and bar length in characteristic panicoid grasses matched those found in the literature: Themeda quadrivalvis and Setaria pumila produced bilobe phytoliths with longer bar lengths in general, whereas Apluda mutica produced a high ratio of polylobes and shorter bilobe phytoliths in comparison to the other two taxa. With little work done on phytoliths from the Southern Arabian highland region, this study presents an introduction to their use as a paleoecological proxy for understanding the ecologies and vegetation communities of the region.



Phytoliths, Archaeobotany, Reference collection, Dhufar ecology